Chemical and palaeoentomological evidence of a relationship between early Eocene Belgian and Oise (France) ambers

Of the early Eocene amber deposits known across the world, Belgian amber has been mostly absent from the relevant literature. We reinvestigated amber held in the palaeobotanical collection of the Royal Belgian Institute of Natural Sciences, Brussels, which derived from three localities in Belgium that originated from two geographical areas (Leval-Trahegnies and Orp-le-Grand). Using Fourier transform infrared (FTIR) spectroscopy we show the close chemical relationship of Belgian amber to the early Eocene Oise amber from the Paris Basin, and highlight the potential effect of weathering on the amber chemistry. The amber derives from a very similar botanical source as the Oise amber (Combretaceae or Leguminosae-Caesalpinioideae), but from different coeval basins. The two Leval-Trahegnies localities provided amber that exhibit different stages of weathering (heavily fissured and crazed, darkened) and lacking any inclusions. The Orp-le-Grand locality provided the least weathered amber, with one amber piece containing two inclusions: a mite and a new genus and species of hemipteran (Cativolcus uebruum gen. et sp. nov.), and a second one that preserved the impression of insect wings pressed into the surface.


Geological age and setting
The ambers from the palaeobotanical collection in the Royal Belgian Institute of Natural Sciences (RBINS, Institut Royal des Sciences Naturelles de Belgique) derive from three amber deposits recovered from two areas: Orp-le-Grand and Leval-Trahegnies (one locality labelled as Sablière La Courte à Leval (M5), and the other as Trieu de Leval (M6)) (Fig. 1a starred).These deposits were listed in the collection as dated to the Landénien supérieur/ upper Landenian, now an obsolete stratigraphic term, or as Sparnacien/Sparnacian (describing a facies).The Belgian ambers studied here have general inventory (IG, Inventaire Général) numbers registered in the collection catalogues of the RBINS, indicating their provenance.The amber labelled as Sablière La Courte à Leval (M5) has the number IG 6978 and that from Trieu de Leval (M6) the number IG 7021, while the Orp-le-Grand amber is identified with the number IG 9875.
In the Leval-Trahegnies area, the Trieu de Leval and Sablière de La Courte (correct name for the Sablière La Courte à Leval) localities are only separated by a few hundred meters.They however show slightly different successions.In the Trieu de Leval locality, first mentioned by Rutot 13 , a thick grey clay deposit is intercalated between chalk deposits of the Late Cretaceous Saint-Vaast Formation and green sands of the Ypresian Carnières Formation corresponding to the Orchie Member of the Kortrijck Formation (the first name has been used by cartographers 14 and defined there but was not yet recognized by the National Commission for Stratigraphy Belgium (NCSB)).By contrast, in the Sablière de La Courte locality, the Saint-Vaast Formation is overlain by a thick layer of cross-bedded sands themselves covered by a layer of grey clay 18 .Both the sand and the clay layers have been eroded by quaternary fluvial deposits.Chauffin 12 later stated that there are two superimposed levels (one Paleocene-and the other Eocene-aged) exposed in quarries in Leval-Trahegnies, but amber has only been reported from the Eocene level in this area 14 .Amber occurs in both localities in lignite beds intercalated within the layer of grey clay.Moreover, in the Trieu de Leval locality, the amber is associated with abundant plant remains including branches and leaves 14 .Originally, only one insect inclusion was mentioned from the Sablière de La Courte locality.It was determined by a local researcher, M. Séverin, as a "hémiptère homoptère de la famille des Jassides", and reported by Rutot 14 .
In these early reports, the determination of the age and of the lithostratigraphy has been matter of debate.Rutot 13 attributes the Trieu de Leval locality to the Montian, an obsolete continental regional stage dated from the early-middle Paleocene, while Briart 15 reported it as the Late Cretaceous Heersian local stage.In an attempt to clarify this point, the above-mentioned leaf flora has been studied by Marty 16 who concluded that the flora was younger than the Cretaceous and likely Paleocene.Due to the intercalation of sands, the Sablière de La Courte locality has been dated as upper Landenian in age 17 .This regional stage would now correspond to the lower Eocene (Ypresian).A better understanding of the geological succession in the region has allowed the determination that both deposits were part of the same geological formation.Older literature attributes both of the Leval localities to the Tienen Formation 17 , however, the most recent data places them within the contemporaneous Erquelinnes formation 18 .The latter formation has not yet been recognized by the NCSB but as it is used in the most recent publication 18 we prefer to mention both names.This formation is unofficially divided in two members: the sandy La Courte Member and the Leval Member that is made of grey clays.It is within the Leval Member that the amber occurs.The depositional setting for both the Leval-Trahegnies and Orp-le-Grand geographical areas are interpreted as fluvio-lacustrine sediments rich in organic matter 19 corresponding to a swampy environment 18,20 .
The amber from the Tuillerie of the Orp-le-Grand locality is first mentioned by Stockmans 21 but, as far as we know, no detailed account was ever published on this locality.Despite the lack of stratigraphic description, the stratigraphic unit positioning of Defino & Smith (see Fig. 4 of Delfino & Smith) 19 indicates that the amber deposit can be attributed to the upper part of the Tienen Formation.
The base of the Tienen Formation is marked by a carbon isotope excursion (CIE) marking the onset of the Paleocene-Eocene Thermal Maximum (PETM) and therefore recording the Paleocene-Eocene boundary 22,23 .The Tienen Formation has been studied in detail for its fossil content and has been determined as being early Ypresian, early Eocene in age 24,25 , with the Erquelinnes formation considered to have the same age 24 .As the ambers were washed clean before or at the time they came into the collections, there is no additional material such as the host sediment available for palynological dating.

Appearance of ambers from Leval
No inclusions were observed in either the La Courte à Leval (M5) or the Trieu de Leval (M6) ambers.Visually the ambers are both very difficult to screen with light microscopy as they are now very crazed and darkened.The La Courte à Leval (M5) amber is predominantly dark red in colour, and the most crazed and fissured of all the ambers.There are a few yellow opaque pieces, but these constitute a very small proportion of the material.The amber is now mostly angular fragments and was likely mostly unlayered (Fig. 1b top row).The Trieu de Leval (M6) amber shows a mixture of colours from yellow, to orange and brown, with orange-red angular fragments being predominant, the yellow material is opaque.There is very little layered material.As the amber pieces are highly crazed and fissured, it is difficult to see inside the pieces to determine if they are translucent or not (Fig. 1b middle row).

Appearance of amber from Orp-le-Grand
The amber has a more or less uniform high translucency and a medium orange colour, although there is 50 g of yellow and opaque (3.8% by weight) amber pieces present.The majority of the amber is unlayered, fissured and crazed, although this is the least fissured, darkened and crazed amber of the three amber-bearing localities investigated here.There are some stalactite-like and layered pieces in the collection (Fig. 1b lowest row).This is the only amber in the RBINS collections that yielded new fossil inclusions and impressions.

FTIR-ATR analyses of Belgian ambers
In order to understand the potential relationships between and infer any source plant(s) for the Belgian ambers, FTIR-ATR spectroscopy was used to analyze the bulk chemistry, and the results were directly compared with those spectra obtained from Oise (Le Quesnoy quarry) amber samples (Supplementary figure S1).All samples have the characteristic peaks that indicate that all the samples are fossil resins (Table 1, Fig. 2a).
The fingerprint region below 1500 cm −1 can vary greatly in its peaks depending on the amber or resin tested.Here all the ambers tested share peaks at 1447 cm −1 and 1384 cm −1 linked to C-H bending motions of methyl and methylene functional groups, the peaks at between 1300 and 1100 cm −1 are assigned to C-O single bonds and the peak at 887 cm −1 is due to the out-of-plane C-H bending motions in terminal methylene groups [26][27][28][29] .The mean FTIR spectra (Fig. 2a) and the individual spectra (Supplementary figure S1) for the different ambers are almost identical.Furthermore, the Oise and the Belgian ambers all share the same functional groups shown by the presence of the same peaks in their spectra (Table 2, Fig. 2a, Supplementary figure S1).There are small variations in the peak intensities observable (Supplementary figure S1) meaning that the spectra are not completely identical as the peaks vary in intensity, but they all share the same bulk chemistry.

Statistical analyses of the amber spectra
In the multivariate analyses applied to the dataset (both the dataset and R scripting available in the Supplementary Dataset), 89.2% of the variance was accounted for by two principal components (percentage of variance for The PCA (Fig. 2b) shows that the ambers from Leval (Leval (M5) and Leval (M6)) group together, whereas the Orp-le-Grand ambers group separately.The French Oise ambers group together and appear to overlap with a Leval (M5) sample.The loadings for PC1 (Fig. 2c) highlight the spectral regions of similarity and differences between the ambers.Firstly, the ambers share a similar level of resin polymerization, which is noted in the lack of peak intensity around 3400 cm −1 attributed to hydroxyl groups that are used to indicate degrees of resin polymerisation 18 .The intensity of the peaks at 2935 cm −1 and 2848 cm −1 , linked to methylene groups and the large (negative) peak at 1693 cm −1 caused by C-O double bonds in carboxyl groups of resin acids just highlight the band intensity differences between the samples at those wavenumbers.These differences are most likely attributable to either the slightly different taphonomy of the ambers, or their subsequent geological history and varying levels of weathering/oxidation, as noted in the different colourations and levels of oxidised appearance of the ambers from the different localities, or a combination of both.
The locality mean cluster analysis (Fig. 2d) highlights the grouping of the ambers from Leval, Belgium as they form one cluster, with amber from Orp-le-Grand forming a second cluster with Oise amber from France.This appears to mirror the colouration and level of oxidation noted for the ambers from each locality, with the ambers from Leval being the most darkened and oxidized (heavily fissured and cracking), whereas the ambers from Orp-le-Grand (Fig. 1b) and Oise are generally lighter and less oxidized in appearance.Additional amber spectra were included to broaden the coverage of the dataset and the results remain very similar, supporting the initial inferences (Supplementary figure S2).Further cluster analyses (Supplementary figure S3) treating each sample spectrum individually has two main groupings recovered in all cases for the Belgian and Oise ambers.There is a consistent separate grouping of the Leval M5_2, Leval M6_1 and Leval M6_3 spectra, suggesting that these ambers from the two Leval localities are not as distinct as represented by the mean cluster analysis shown in Fig. 2d.This could be because these three amber samples looked more alike in terms of colouration and crazing than the other ambers tested.

Inclusions and impression in amber
The only amber inclusions found to date are from one amber piece derived from the Orp-le-Grand locality (Fig. 3a-d).In this amber piece (BE-RBINS-ENT-AMBER-IG-34605) two inclusions were discovered.The larger (2.5 mm long) and better-preserved inclusion is of a hemipteran Cativolcus uebruum gen.et sp.nov.(Fig. 3a-c).
The syninclusion is a mite (Fig. 3d), approximately 1.2 mm long but the development of pyrite has obscured most of the details of the specimen, preventing further identification.In addition to these inclusions, the impression of insect wings is preserved pressed into the surface of a separate stalactite-shaped amber piece (Fig. 3e).

Comparison of Belgian ambers with Oise amber
FTIR analyses of Oise and Belgian amber samples showed that overall, the spectra from all localities are very similar (Fig. 2a, Supplementary Fig. 1), whereas the PCA (Fig. 2b) highlights that both sets of samples from Leval group together as they share a very similar origination and geological history.The Orp-le-Grand amber is more distinct, perhaps indicating a slightly different depositional environment and/or geological history (Fig. 2b, c).It also strongly suggests that there is an effect from degrees of weathering/oxidation being detected.The less heavily weathered Orp-le-Grand amber is more distant (Fig. 2d) to both more heavily weathered and darkened samples from Leval (compare colouration in Fig. 2b).The overall lighter, less crazed and fossiliferous amber from Orp-le-Grand clusters with Oise amber (Fig. 2d) suggesting they have the most similarity in bulk chemistry.
In any case, this hints at the potential source plant being similar or even identical and similar environmental settings.As the samples from Orp-le-Grand are the least weathered of the Belgian ambers and the Oise sample appeared unweathered at the time of measurement, the level of weathering/oxidation in the Leval samples may account for their greater distance from the other samples (Fig. 2d).It is not likely that the apparent similarity between the Orp-le-Grand and Oise ambers results from a very closely shared geological history given that the Leval ambers, not the amber from Orp-le-Grand, are actually palaeogeographically closer to the Oise amber from the Paris Basin in France (Fig. 1).
Oise amber from France was first described by Lacroix 30 , and is thought to derive from the tree Aulacoxylon sparnacense (Combretaceae or Leguminosae-Caesalpinioideae) based on associated anatomically preserved Table 2. Peaks and functional group interpretation of the Belgian and Oise amber mean FTIR-ATR spectra, v, stretching; as, asymmetric; s, symmetric; δ, in plane bending.data compiled from Tappert et al. 26 Beltran et al. 27 , Lyons et al. 28 , Pretsch et al. 29 .woods 6,7 .Biomarker analysis of the amber identified the diterpene quesnoin, suggesting an affinity of the resin with Caesalpinioideae 31 .Nohra et al. 32 confirmed an angiosperm amber source plant with likely fabacean affinity for Oise amber.Given the similarity of the FTIR spectra of Belgian and Oise ambers, we suggest that the Belgian ambers most likely have a similar or even identical Leguminosae-Caesalpinioideae botanical source (Fig. 2, Supplementary figure S1).
In addition to the ambers, notable similarity exists in the contemporaneous vertebrate faunas reported from localities in Belgium that are very close to the Belgian amber localities 5,[33][34][35] .Dormaal, near Orp-le-Grand, is the reference-level MP7, the earliest European locality from the early Eocene 23,[33][34][35] and is correlated with Erquelinnes (near Leval-Trahegnies) and Le Quesnoy in France from which Oise amber derives.This adds independent evidence that these Belgian and French localities, and their ambers, were of comparable age and with similar environments and ecosystems.

Inclusions in Belgian amber
Despite the very small amount of amber held in the palaeobotanical collections of the Royal Belgian Institute of Natural Sciences (7.9 kg from Leval in total and 1.3 kg from Orp-le-Grand), two inclusions in one amber piece and insect wing impressions on another were discovered from the Orp-le-Grand locality.The fissured and crazed surfaces of the Leval amber made it hard to be certain that there were no inclusions, but we could not discern any.We exclude the possibility that the newly discovered inclusions are the missing ones previously reported by Langeron 11 , as those historic specimens are reported from amber deriving from Leval, not Orp-le-Grand.We do not know the whereabouts of the insect inclusions from Leval reported by Langeron 11 .
The degradation of the mite inclusion through pyrite decay means that a closer identification is not possible.However, the new hemipteran is not affected by any pyrite, despite being contained in the same amber piece and actually shows excellent preservation.It is unclear why the two inclusions are preserved so differently given that the hemipteran had a clear fissure over its dorsal surface leading down towards the inclusion, but none were noted for the mite.The discovery of a new hemipteran genus and species is unexpected given the small amount of the Belgian ambers present in the palaeobotanical collection and that these ambers are almost completely barren of inclusions.This is particularly notable when compared to the richly fossiliferous and far larger, contemporaneous but completely separate Oise amber deposit from the Paris basin with 350 kg 5 , where Hemiptera comprise 10% of the currently known inclusions in Oise amber 36 .Etymology.Generic name is given after Cativolcus, a king of the Eburones, leader of a Belgic tribe of northeastern Gaul (Gallia Belgica), where modern Belgium is located.Gender: masculine.

Holotype
Male.Specimen BE-RBINS-ENT-AMBER-IG-34605, deposited in the Royal Belgian Institute of Natural Sciences, Brussels, Belgium.Syninclusion: an undetermined mite.Pronotum in dorsal view subtriangular, without calli, anterior margin widely arcuate, lateral margins distinctly diverging posteriad, posterolateral angles widely angulate, posterior margin shallowly concave.Pronotum about 2.8 times as wide (0.82 mm) as long in mid line (0.29 mm); about 1.23 times as long as head in total.Disc of pronotum convex, smooth, covered with moderately short, erected and sub-erected hairs, directed posteriad.
Mesopleura with a few short setae in upper portion.Metapleura smooth, with scent gland area (?) delicately granulose and slit-like opening.
Hemelytra 1.74 mm long, 0.53 mm wide, corium 1.04 mm long, about 2.84 times as long as cuneus (0.36 mm), brownish, covered with moderately short, directed posteriad and lighter than background setae.Claval commisure 0.4 mm long.Hemelytral membrane with two cells, one small and one large, surface delicately crumpled; membrane 1.59 times as long as wide.
Male terminalia.Genital capsule (pygophore) entire, trapeziform in outline, smoothly rounded towards apex, covered with long setae; ventral margin with subtriangular process medially.Left paramere smaller than right one, elongate and rounded apically.Right paramere large, bent at base, with apical spine-like processes.

Remarks
Psallopinae is the smallest subfamily within the true bugs family Miridae, including two extant genera -Psallops Usinger, 1946 42 with 19 extant and 3 extinct species and Isometocoris Carvalho et Sailer, 1954 43 with 2 recent species.The latter genus was proposed to be moved to Cylapinae, and Psallopinae reduced to tribe in Cylapinae 44 , but this action is not universally accepted 45,46 .In addition, extinct genera were described (Cylapopsallops Popov et Herczek, 2006 39 , Epigonomiris Herczek et Popov, 1998 41 48 , habitats and habits are also poorly known, some species were collected at light, others by Malaise traps and net sweeping, with suggestion of their nocturnal habits.Some psallopinous bugs from Thailand have been found under half-detached bark fragments of fabaceous broad-leaf plants 49 .The psallopines are assumed to be also predaceous, similarly to related plant bugs of subfamily Isometopinae, which are also considered to be bark-inhabitants, as they are also documented under detached bark fragments, and prey on scale insects or other tiny arthropods 50,51 .Psallopinae is most probably a relict group that is closely related to the subfamily Isometopinae or Cylapinae 44,46,[52][53][54] .Isometopinae, Psallopinae and Cylapinae should constitute a single clade, and these subfamilies are considered to be the basal ('primitive') groups among the other plant bugs Miridae 55,54,56 .Findings of fossil of Psallopinae in the amber of Oise and in the amber of Orp-le-Grand, Belgium, are for the moment the oldest fossil records of the group.Cativolcus uebruum gen.et sp.nov.from Belgian amber presents combination of such characters as enlarged eyes covering the greater part of the head, antennae placed at the inner sides of the eyes, reduced ocelli, the trapezoid pronotum, 2-segmented tarsi, placing it in Psallopinae.Recent Psallopinae are recognized by eyes occupying most of the head, the narrow vertex, the smooth body surface, the finely upturned anterior margin of the pronotum, subdivision of labial segment 4, the subapical tooth on the claws, tarsi 2-segmented, and membrane with single or two cells 46 .Large compound eyes are present in both species of Cativolcus gen.nov., such conformation of compound eyes is to be considered as the main apomorphic character supporting the clade Psallopinae + Isometopinae.The occurrence of ocelli is regarded as the plesiomorphic condition 57 , these are absent in Cativolcus gen.nov, therefore it could be derived condition of this fossil.Schuh & Schwartz 52 suggested that loss of the ocelli in Psallopinae and Cylapinae could be convergent.Among the Miridae, presence of three-segmented tarsi is considered as the plesiomorphic condition 46,52,58 , however pseudotrimerous and dimerous tarsi are not exceptional in this family.Thus, this character is at least homoplasic 37 .With the present state of knowledge, it is hard to assess the phylogenetic value of morphological characters usually used as diagnostic for Psallopinae and its taxa.The most recent molecular phylogenetic results presented by Oh et al. 54 , suggested splitting of Isometopinae and Cylapinae in the earliest Cretaceous, alas Psallopinae were not taken to the analysis.The recent Psallopsinae live under very different climates even though all are warm, therefore it could be inferred that Cativolcus uebruum gen.et sp.nov., also inhabited a warm climate, which is in concordance for the palaeoconditions reconstructed for the fossil site and was present at a time of global warming when the resin was originally exuded entrapping the specimen.

Conclusions
Early Eocene amber held in the palaeobotanical collection of the RBINS, Brussels, is from three localities across two geographical areas of Belgium.Using FTIR-ATR we showed these ambers to be chemically very similar to each other and to the contemporaneous Oise amber from France, suggesting that they share the same or a very similar botanical source (Combretaceae or Leguminosae-Caesalpinioideae).Ambers from the two different deposits of Leval-Trahegnies are more weathered in appearance (darkened and heavily crazed surfaces of the amber pieces) and they lack inclusions.The amber from Orp-le-Grand is, in comparison, less weathered as it is generally lighter in colour and less crazed in appearance than the Leval-Trahegnies derived amber.Although a smaller volume of amber is present from Orp-le-Grand, two inclusions were discovered in one piece, plus the impression of insect wings on the surface of another.The inclusions are a mite and a new genus and species of hemipteran (Psallopinae) Cativolcus uebruum, representing the shared oldest occurrence of the Psallopinae with that reported from the relatively palaeogeographically close by Oise amber from the Paris basin.

Material and historic localities
In the palaeobotanical collection of the Royal Belgian Institute of Natural Sciences (RBINS, Institut Royal des Sciences Naturelles de Belgique), Brussels, Belgium, there is amber collected from three localities which appear in the inventory as (1) Sablière La Courte à Leval (M5), (2) Trieu de Leval (M6), both from the Mons Basin, Leval-Trahegnies, near Morlanwelz in Hainaut Province, and (3) Orp-le-Grand, in the Walloon Brabant Province (Fig. 1 starred).The former amber-bearing localities have since been closed and filled in and thus cannot currently be accessed.

La Courte à Leval (M5)
Notes from the RBINS collections record the M5 locality as 'La Courte à Leval, Morlanwelz 5, Sablière la Courte à Leval-Trahegnies.Landénien Supérieurʼ.In the present analyses it is referred to as 'Leval M5' .This amber was found in clay lenses in the sand quarry at La Courte à Leval.The whole deposit in the museum is marked with RBINS number Plateau PBot 6754 (67,939) and IG 6978.There is 4902 g of amber that has been washed and graded by size.

Trieu de Leval (M6)
The M6 locality is listed as 'Trieu de Leval, Morlanwelz 6 Carrières d'argile plastique du Trieu de Leval à Leval-Trahegnies, Landénien Supérieurʼ.In the present analyses it is referred to as 'Leval M6' .The whole deposit in the museum is marked with RBINS number Plateau Pbot 6807 (67,903) and IG 7021.2988 g of amber in total was recovered from a clay quarry, and has been washed and sorted by size.

Orp-le-Grand
This amber locality is noted as 'Orp-le-Grand, Argilière des Tuileries, Jauche 1, Landénien Supérieurʼ.In the present analyses it is referred to as 'Orp le Grand' .The whole deposit from the Walloon Brabant Province in the museum is marked with RBINS number Plateau PBot 6808 and IG 9875.There is 1309 g of amber in total, which has been washed, sorted and selected by the seller of the amber who was the foreman of the quarry.The amber from this locality was sold to the museum in three separate lots (sometimes with other fossil materials).The IG number for Orp-le-Grand amber shows that it corresponds to the purchase on December 2, 1932 of mammal, reptile and fish bones as well as fossil resin from the brick and tile factory of Orp-le-Grand (pers.comms.The amber was observed and initially screened for inclusions with a light microscope using both transmitted and incident light.All insect remains and impressions were found in the amber from Orp-le-Grand.As the amber is extremely brittle and the hemipteran inclusion was exposed very close to the surface of the amber with a fissure exposing part of the specimen, the amber specimen was stabilized by applying a very thin coat of high-grade epoxy resin (Epo-Tek 301-2, Epoxy Technology, Billerica, Massachusetts, USA), that also sealed the existing fissures (see Sadowski et al. 59 , for protocols), before minor and careful grinding and polishing of the specimen.Grinding and polishing manually with wet silicon carbide papers (grit from 25.8 to 5.0 μm particle size; Struers company, USA) was done to remove scratches and to create a smooth surface parallel to the inclusion.The amber inclusions were examined with a Stereo Discovery V8 dissection microscope (Carl Zeiss, Germany) and an AxioScope A1 compound microscope (Carl Zeiss, Germany) using incident and transmitted light simultaneously.Images were taken with Canon EOS 5D digital cameras (Canon, Tokyo, Japan) attached to these microscopes.Additional photographs were taken at the Laboratory of Evolutionary Entomology and Museum of Amber Inclusions at the University of Gdansk, with an Olympus BX51 microscope (Olympus, Tokyo, Japan), equipped with a Canon EOS 90D digital camera (Cannon Tokyo, Japan) abd ab Oympus EP50 camera.The images were then stacked using HeliconFocus version 6.3.3Pro (Helicon Soft, Kharkov, Ukraine).Some images are composites of several stacked images stitched together using Adobe Photoshop.For the insect wing impressions, the images were taken using a Stemi 508 dissecting microscope (Carl Zeiss, Germany) with incident light and the images stacked using Photoshop.Drawings were made with the use of camera lucida attached to the Olympus BX51 and Olympus SZX10 microscopes then readjusted with the CorelDrawX7 package (Corel, Ottawa, Canada).

FTIR and statistical analyses
Samples of the Belgium ambers (three per locality were allowed by RBINS, Supplementary Fig. 1) along with comparison samples of Oise amber deriving from the Le Quesnoy quarry (Paris Basin) (three samples measured, Supplementary Fig. 1), plus samples of Baltic succinite and Burmese amber (Supplementary Fig. 2), were finely powdered separately prior to measurement.The spectra were collected as detailed in Seyfullah et al. 60 , using attenuated total reflection (ATR) mode with a Bruker Platinum A225 diamond ATR accessory installed on an FTIR spectrometer (Bruker Vertex 70), in absorbance with 32 scans collected for each sample with a spectral resolution of 4 cm −1 in the range from 4000 to 650 cm −1 .Background spectra were taken before each analytical run and automatically used to correct for background from the sample spectra.Each sample was measured three times to ensure consistency and three samples of the different ambers were used in total.Bands were identified by comparison with previous reports [26][27][28][29] .The ATR crystal and anvil were thoroughly cleaned between each measurement.The spectra were visualized using SpectraGryph v1.2.13.The spectra were then subjected to statistical analyses.
All data manipulation and analysis were carried out in R version 4.1.0 61with the packages baseline version 1.3-1 62 and RColorBrewer version 1.1-2 63 .The dataset and R script are available in the supplementary information.Each spectrum was standardized to zero mean and unit variance (z-scores) using the equation (x−x)/σ, where x is the absorbance value, x̄ is the spectrum arithmetic mean, and σ is the spectrum standard deviation.The baseline was corrected using a modified polynomial fitting with a second order polynomial baseline 61 .
For the multivariate data exploration and visualization principal component analysis (PCA) and cluster analysis were used 64 .The cluster analysis was run using the Euclidean distance and with the unweighted pair group method with arithmetic mean (UPGMA) linkage algorithm and the locality-mean spectra were also subject to this to simplify relationships between the amber samples from the different localities.Other clustering options were also run.The datasets and the R scripts are available as Supplementary data.

Terminology and taxonomy
This publication and the nomenclatural acts it contains are registered in ZooBank, the proposed online registration system for the International Code of Zoological Nomenclature (ICZN).The ZooBank LSIDs (Life Science Identifiers) can be obtained and the associated information viewed using any standard web browser by appending LSID to the prefix 'http:// zooba nk.org/' .The LSID for this publication is: urn:lsid:zoobank.org:pub:BB11FBB1-5FEC-4994-A8B2-0DAD2D082B70.

Figure 1 .
Figure 1.Ambers from Belgium.(a) map of Belgium and surrounding area, with the Eocene amber-bearing localities represented in the RBINS collections (starred).Ger.-Germany, Lux.-Luxembourg, Neth.-Netherlands.(b) Eocene ambers from Belgium, top row, amber from Sablière La Courte à Leval (M5), this is the most darkened and fissured amber from the three localities, with some variations in colour; middle Row, amber from Trieu de Leval (M6); lowest row, amber from Orp-le-Grand showing the lightest colour of amber present from each of the three localities.Scale bar 20 mm.
Head with compound eyes about 2.6 times wide as long (0.225 mm).Eyes large, discoid, occupying nearly entire sides of head, contiguous with anterior margin of pronotum and with anterior margin of vertex.Vertex narrow (0.09 mm , 0.14 mm wide at base, 0.09 at apex), about half as width of compound eye, covered with moderately long, protruding setae.Frons and clypeus narrow, covered with moderately long, protruding setae.Clypeus smoothly flush with convex frons, about twice as long as wide; base of clypeus located slightly above than half eye height; mandibular plate (jugae) carinate, relatively broad, nearly reaching apex of clypeus.Ocelli absent.Antennal fossa situated at base of maxillary plate, emarginated, at about lower 1/3 of compound eye.Antenna 4-segmented, I antennomere 0.125 mm long, calyculate, narrow at base, slightly widening apicad; antennomere II the longest, 0.453 mm, about as wide as I antennomere, covered with dense, slightly protruding setae, longer than diameter of antennomere; III antennomere 0.281 mm long, narrower than II antennomere, covered with dense slightly protruding setae, longer than diameter of antennomere, apical antennomere, the IV, shorter than preapical one, 0.193 mm, narrowed at base, cigar-shaped, widening than tapering apicad, covered with slightly protruding setae, longer than diameter of antennomere, with single thicker seta in basal half.Rostrum 4-segmented, slightly exceeding apices of metacoxae; apical segment subequal to preapical one (ca.0.24 mm).